Photoinitiated curing of olefinically unsaturated compositions has a broad spectrum of industrial uses including polymer synthesis, elastomer vulcanization and the curing of adhesives, coatings and films. Typically the photoinitiators in such systems have primary activity in the ultraviolet (UV) region, with little or no visible light sensitivity. While this is often a useful property, e.g., when the composition needs to be stored or preapplied under conditions subject to visible light exposure, there are many applications in which it is desirable that a composition be cureable by exposure to visible light. For instance, in adhesive applications when bonding polymers which are transparent to visible light but not to UV light, effective visible light photoinitiators are particularly desirable. Polycarbonates are examples of such visible light transparent, UV light opaque polymers.
In other applications visible light initiated curable compositions are desirable because visible light is much cheaper and safer to produce than UV and requires less specialized equipment.
L. Thijs, S. Gupta, and D. Neckers, J. Org. Chem., 44 4123 (1979), describe the synthesis and use of t-butyl peresters having an associated benzophenone chromophore as photoinitiators. These authors suggest that the photodecomposition characteristics of these perester compounds can be altered by the absorption characteristics of the associated chromophore. The same authors published subsequent papers, J. Polymer Sci., 19, 103-114 and 855-868 (1981), in which the photoinitiating characteristics of other benzophenone peresters are examined.